Heretofore, magnetic recording media such as a magnetic tape, a floppy disk, and so on, are produced generally by the steps of: applying a coating composition prepared by dispersing magnetic fine particles in a resin dissolved by an organic solvent onto a running belt-like flexible support; orienting to desired direction easily-magnetizable axes of the fine magnetic particles in the coating composition applied on the support, drying and solidifying the applied coating composition, and surface-treating the resulted coating layer such as calendering, thereby obtaining a belt-like magnetic recording medium; and slitting, cutting or punching the belt-like magnetic recording medium to obtain a magnetic tape having a desired width or a magnetic disk having a desired shape.
Recording a large amount of information in a limited recording area, that is, high-density recording, has been required increasingly of magnetic tapes and floppy disks. Reduction in the size of a magnetic head therefore has been desired because the magnetic flux generated from the magnetic head must be concentrated in a fine area. The volume of the magnetic layer capable of inverting the direction of magnetization decreases with the reduction in generated magnetic flux caused by minimizing the size of the magnetic head. Therefore, it is necessary to thin the magnetic layer for the purpose of obtaining high-density recording.
Although it is necessary in high-density recording to thin the magnetic layer beyond that found in the magnetic layer of a conventional recording medium, in the case where such a thin film is formed singly, not only is it very difficult to form a faultless uniform coating but also it is nearly impossible to perform sufficient orienting treatments because drying/solidification of the layer is completed rapidly.
To solve that problem, for example, Japanese Patent Unexamined Publication No. Sho-62-212933 proposed a method of the type in which, as shown in FIG. 9, a simultaneous multilayer coating apparatus 8 applies a lower-layer magnetic coating composition 3 and an upper-layer magnetic coating composition 4 onto a nonmagnetic support 2 drawn out of a feed roll 1; an orientation apparatus 5 performs an orienting treatment while the two layers are not yet dried; a drier 6 dries the layers; and the resulting support is taken up by a takeup unit 7. It is asserted that orientation of ferromagnetic fine particles in the upper thin magnetic layer is obtained.
Heretofore, it is in most cases difficult to orient magnetic fine particles obliquely compared with the general in-plane orientation of conventional materials (lengthwise orientation). Japanese Patent Unexamined Publication No. Hei-2-146106 asserted that orientation of particles can be performed securely when in-plane orientation is performed with an electromagnet for lengthwise orientation before a magnetic recording medium 11 in a wet state is subjected to oblique orientation by a permanent magnet 10 for oblique orientation as shown in FIG. 10.
However, when magnetic fine particles in a high wet state (a low dry state) are oriented strongly, the magnetic fine particles tend to aggregate. Thus, the magnetic fine particles are distributed unevenly on the support. If, on the other hand, magnetic field intensity for orientation is lowered to avoid aggregation, the size of the apparatus for orienting the particles must be increased greatly to obtain sufficient orientation.